Crucible

Abstract

A crucible of a resistive material has a smoothly rounded inner bottom and a radially outer portion of the outer bottom having a rounded shape. The shape of the outer bottom bears a predetermined relationship to the shape of the inner bottom. In one embodiment of the invention, the outer bottom and inner bottom have a common radius of curvature, whereby the thickness of material between the outer and inner bottom is constant. In a second embodiment of the invention, the centers of curvature differ, whereby the resistivity of material at differing radii is tailored.

What I claim is: 
     
       1. A crucible of a resistive material comprising: an annular side wall having an open top end and a closed bottom;   said bottom including a concavely rounded inner surface with a first curvature;   said bottom including an outer surface;   at least a radially outer portion of said outer surface joining said annular side wall being convexly rounded with a second curvature;   said first and second curvatures having a functional relationship to each other; and   said funtional relationship includes centers of curvature of said first and second curvatures being displaced from each other, whereby a thickness of said bottom between said inner and outer bottoms varies smoothly.   
     
     
       2. A crucible according to claim 1 wherein said thickness becomes smaller at increasing radii. 
     
     
       3. A crucible according to claim 2 wherein said thickness decreases in a functional relationship effective to maintain a resistivity of said resistive material constant at all radii. 
     
     
       4. A crucible according to claim 1 wherein said first and second curvatures are figures of rotation of parts of circles. 
     
     
       5. A crucible according to claim 1 wherein said outer bottom includes a button centered therein. 
     
     
       6. A crucible according to claim 1 wherein said outer bottom includes a horizontally extending surface centered in said outer surface. 
     
     
       7. A crucible according to claim 6 wherein said outer bottom includes a button centered in said horizontally extending surface.